Foundations of canonical update support for closed database views

Abstract

A closed view of a database schema is one which is totally encapsulated. Insofar as the user is concerned, the view is the database schema. The rest of the database system is not visible through the view, and is is not required for complete use of the view. Similarly, the updates which may be effected through the view have their scope limited entirely to that view. In this paper, we lay the mathematical foundations for the systematic support of such views. The proper context is shown to be that of update translation under constant meet complement, a refinement of the constant complement strategy of Bancilhon and Spyratos. The central complexity result for relational schemata is that checking the legality of updates is "infinitely" simpler than blindly checking that the new state is legal for the view schema, and in the particular case that the base schema is constrained by functional dependencies, may always be performed in constant time, even if the view schema is not finitely axiomatizable. We further establish that, under very natural assumptions, update strategies for closed views are unique.

Consistent Web site updating based on bidirectional transformation

“…Bidirectional transformation [10], originating from the view-updating technique in the database community [3,5,11,12,16], involves a pair of transformations between a source and its view: the first transformation, called forward transformation, maps sources to views and is used to reflect changes in a source in its view. The second transformation, called backward transformation, maps views to sources and is used to reflect changes in a view in its source.…”

“…Our design of the Web site maintenance system, Vu-X, based on bidirectional transformation was greatly inspired by pioneering work [10,4] on data synchronization based on bidirectional transformation, which originated from work on view updating [3,5,11,12,16] in the database community, where modifications to view could be reflected back to the original database. We borrowed this technique to enable Web site maintenance with one significant extension: editing operations can not only modify the view but also the transformation code, which has not been exploited before.…”

“…Bidirectional transformation has many practical applications including the synchronization of replicated data in different formats [10], presentation-oriented structured documents development [13], interactive user interface design [18], coupled software transformation [14], and the wellknown mechanism for view updating, which has been intensively studied in the database community [3,5,11,12,16].…”

Characterization of desirable properties of general database decompositions

“…While here we study properties of decompositions in which the component schemata have nontrivial constraints connecting them, [17] examines direct decompositions, in which all views are independent. The paper [18] also deals with decompositions in a general context, but focuses upon the problem of updates rather than schema desirability. This paper began as the full version of the conference paper [19].…”

FD Covers and Universal Complements of Simple Projections

“…14 and Thm. 14], although a specific characterization in terms of the meet is first presented in [12] and refined greatly in [13], where it is also shown that for the case of projections of relational schemata constrained by usual database dependencies, state invariance is obtained precisely in the case that a cover of the dependencies of the main schema embed into the two views [13,Prop. 2.17].…”